CVE-2013-4238

CVE-2013-4238 is a medium-severity vulnerability in Python with a CVSS 2.0 base score of 4.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

• Severity: Medium (CVSS 2.0 base score 4.3)
• EPSS exploit prediction: 5% (92nd percentile)
• Actively exploited: Not listed in CISA KEV
• Weakness: CWE-20
• Affected product: Python
• Published: 2013-08-18
• Last modified: 2026-06-16

Description

The ssl.match_hostname function in the SSL module in Python 2.6 through 3.4 does not properly handle a '\0' character in a domain name in the Subject Alternative Name field of an X.509 certificate, which allows man-in-the-middle attackers to spoof arbitrary SSL servers via a crafted certificate issued by a legitimate Certification Authority, a related issue to CVE-2009-2408.

Frequently asked questions

What is CVE-2013-4238?

The ssl.match_hostname function in the SSL module in Python 2.6 through 3.4 does not properly handle a '\0' character in a domain name in the Subject Alternative Name field of an X.509 certificate, which allows man-in-the-middle attackers to spoof arbitrary SSL servers via a crafted certificate issued by a legitimate Certification Authority, a related issue to CVE-2009-2408.

How severe is CVE-2013-4238?

CVE-2013-4238 has a CVSS 2.0 base score of 4.3, rated medium severity.

Is CVE-2013-4238 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 5% (92nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2013-4238?

CVE-2013-4238 primarily affects Python. In total, 37 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2013-4238?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2013-4238 published?

CVE-2013-4238 was published on 2013-08-18 and last updated on 2026-06-16.

References

• http://bugs.python.org/issue18709
• http://lists.opensuse.org/opensuse-security-announce/2020-01/msg00040.html
• http://lists.opensuse.org/opensuse-updates/2013-09/msg00026.html
• http://lists.opensuse.org/opensuse-updates/2013-09/msg00027.html
• http://lists.opensuse.org/opensuse-updates/2013-09/msg00028.html
• http://lists.opensuse.org/opensuse-updates/2013-09/msg00029.html
• http://lists.opensuse.org/opensuse-updates/2013-09/msg00042.html
• http://lists.opensuse.org/opensuse-updates/2013-09/msg00043.html
• http://rhn.redhat.com/errata/RHSA-2013-1582.html
• http://seclists.org/fulldisclosure/2014/Dec/23
• http://www.debian.org/security/2014/dsa-2880
• http://www.securityfocus.com/archive/1/534161/100/0/threaded
• http://www.ubuntu.com/usn/USN-1982-1
• http://www.vmware.com/security/advisories/VMSA-2014-0012.html
• https://bugzilla.redhat.com/show_bug.cgi?id=996381

Affected products (37)

• cpe:2.3:o:canonical:ubuntu_linux:10.04:-:lts:*:*:*:*:*
• cpe:2.3:a:python:python:2.6.1:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.6.2:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.6.3:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.6.4:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.6.5:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.6.6:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.6.7:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.6.8:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.6.2150:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.6.6150:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.7.1:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.7.1:rc1:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.7.2:rc1:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.7.3:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.7.1150:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:2.7.1150:*:*:*:*:*:x64:*
• cpe:2.3:a:python:python:2.7.2150:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.0:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.0.1:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.1:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.1.1:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.1.2:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.1.3:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.1.4:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.1.5:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.1.2150:*:*:*:*:*:x64:*
• cpe:2.3:a:python:python:3.2:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.2:alpha:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.2.3:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.2.2150:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.3:*:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.3:beta2:*:*:*:*:*:*
• cpe:2.3:a:python:python:3.4:alpha1:*:*:*:*:*:*
• cpe:2.3:o:opensuse:opensuse:11.4:*:*:*:*:*:*:*
• cpe:2.3:o:opensuse:opensuse:12.2:*:*:*:*:*:*:*
• cpe:2.3:o:opensuse:opensuse:12.3:*:*:*:*:*:*:*

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Threat intelligence

Threat-intel indicators referencing this CVE:

• 121.164.135.251 (ipv4-addr)